Management of Ponds,
Wetlands, and Other Water Reservoirs to Minimize Mosquitoes

Introduction:

The recent discovery of West Nile
virus in Indiana has directed
increased attention to mosquitoes (carriers and transmitters of the disease)
and potential means of controlling mosquito populations.Because mosquitoes are known to breed in
standing water, many people are raising questions about the role of natural and
artificial ponds and wetlands in relation to mosquito populations.

In addition to beautifying the landscape, ponds and wetlands
provide important ecosystem services in Indiana
such as storm water management, habitat for aquatic life, and ecosystem health
and stability.Ponds and wetlands reduce
storm water runoff problems by catching and slowing the movement of storm water.They help filter and clean rainfall and
runoff water, and increase ground water aquifer recharge.Ponds and wetlands in the landscape provide
for a diverse flora and fauna, including birds, bats, aquatic insects, fish,
and amphibians; all of which feed on mosquitoes.In addition to these positive aspects, ponds
and wetlands provide recreational outlets for many Hoosiers, including fishing,
swimming, boating, and hunting.

Although under some circumstances ponds and wetlands can
increase mosquito populations, predators of mosquitoes such as fish and other aquatic
organisms will usually control mosquito populations if the pond or wetland
supports a well-balanced ecosystem.This
publication describes problems that make ponds and wetlands especially inviting
to mosquitoes and how to develop and promote an ecosystem in your pond or
wetland that controls mosquito populations by natural predation.

Management of ponds to minimize mosquitoes:

Large & Natural Ponds

A well-functioning pond is characterized by a living
ecosystem that includes fish and other aquatic organisms, stable banks with
good plant cover, and a diversity of insect and animal life.Such a pond will have water with adequate and
stable levels of oxygen, some surface wave action, and possibly a slight
greenish tint from the presence of phytoplankton.In balance, phytoplankton
provide the base of the aquatic food chain and are essential to a pond
ecosystem.Ecologically stable ponds normally
do not produce problem mosquito populations because natural factors of fish
predation and surface wave action tend to kill mosquito larvae.Ponds stocked with fish, such as Large Mouth
Bass and Blue Gill, will greatly reduce or eliminate mosquito larvae.

Bats and Purple Martins consume mosquitoes,
although field research has shown that they do not have significant effects on
mosquito populations1, 2.However, these species should be encouraged as
they help complete a diverse ecosystem.Other
birds, aquatic insects, dragonflies, fish, and amphibians all consume
mosquitoes and their larvae and together serve as natural mosquito control.

In addition to fish, wave action or water movement on the
pond surface is an important factor in reducing mosquito larvae survival rates.Natural ponds and most Indiana
farm ponds will have adequate surface water movement and do not require
additional aeration.In the case of stagnant
ponds lacking water movement, or ponds lacking enough oxygen for fish survival,
mechanical aerators can help improve the pond condition.

Ponds receiving excess nutrients can favor algae blooms and submersed
aquatic vegetation.This situation can
lead to increased mosquito egg laying in these ponds
and pools due to excess plant cover providing the larvae with protection from
predators, wave action, and rainfall3.Mosquito larvae also feed on organic debris
in water.These problem ponds need to be
addressed by restoring the pond with aeration and stocking it with fish.For more information on pond aeration and
restoring water movement contact one of the resource people listed at the end
of this publication, or view the following web publication: http://agpublications.tamu.edu/pubs/efish/370fs.pdf.Avoid the use of fertilizer within at least a
50 foot radius of ponds since this will help prevent excess nutrients from
entering the ponds.

Make sure that high quality vegetative
buffers are in place around ponds.This
will slow or trap sediment, pesticides, and nutrients.Encouraging natural vegetation on the banks and
shoreline of larger ponds may provide some adult mosquito habitat, however it
also has many benefits for pond quality.Tall vegetation surrounding a pond makes it less attractive to geese.Large numbers of geese can degrade pond water
quality and have also been implicated as vectors of West Nile
virus4.In addition, natural
vegetation surrounding large ponds provides habitat for predators of adult
mosquitoes and their larvae.

A balance must be struck between open water and aquatic vegetation.A good rule of thumb is to have 30% of the shallow
area of the pond in rooted-floating and submersed aquatic vegetation.These aquatic plants provide necessary
habitat for fish and other wildlife and should be protected.The side slope of ponds influences the
presence of submersed and rooted-floating aquatic plants.For more information on pond side slope and
construction see the contact list on page 6 under the section: “Assistance with
pond and wetland restoration and management”.

For information on controlling invasive aquatic plants refer
to the following Purdue Extension publications; Aquatic
Plant Management WS-21 http://www.agcom.purdue.edu/AgCom/Pubs/WS/WS_21.pdf,
Barley Straw for Algae Control APM-1-W
http://www.btny.purdue.edu/Pubs/APM/APM-1-W.pdf, and Control of Duckweed and Watermeal
APM-2-W http://www.btny.purdue.edu/Pubs/APM/APM-2-W.pdf.

SmallBackyardWaterGardens &
Shallow Ponds

Small or very shallow ponds are prone to mosquito problems
if they lack fish, water movement, or have their edges or surfaces completely covered
with aquatic plants.If a small pond
becomes stagnant restore water movement with a fountain, waterfall, or other
aerator and stock the pond with minnows.Top feeding minnows will provide effective mosquito control in small
ponds.A small fish that has received a
lot of media attention is the Mosquito fish (Gambusiaaffinis).They have been shown to be the most effective
fish for mosquito control in ponds not connected to natural waterways5, 6.However, Mosquito fish do eat and affect
habitat resources at varying levels and should not be considered for ponds
connected with natural waterways7.

As water temperature rises it holds less oxygen.This may have a deleterious effect on fish in
small and shallow ponds during summer months.Providing afternoon shade from hot summer sun for small and shallow
ponds can improve conditions for fish by helping to keep water temperature from
rising beyond the capacity of fish to tolerate.Artificial aeration will also help improve oxygen levels in small ponds.If mosquitoes are a problem, mowing around
small backyard or shallow ponds may be necessary in order to eliminate adult
mosquito habitat.Clippings from mowed
vegetation can cause problems if they end up in the pond since they add excess
nutrients and provide additional food and protection for mosquito larvae8.Make sure that clippings are prevented from
entering the pond.For more information
on backyard water gardens view this web publication http://wildlife.tamu.edu/publications/TAEXPonds/789a.pdf.

Storm Water Ponds & Infiltration Areas

Ponds that have been built specifically for catching and
holding storm water have important environmental benefits.When properly designed and managed these
storm water ponds and infiltration areas should not become problem mosquito
breeding habitat8.However,
there are conditions under which these areas can encourage mosquitoes.When storm water holding ponds become nearly
dry, vector mosquitoes may invade the ponds.Large fluctuations in water levels of storm water ponds can make the
system ideal for floodwater mosquitoes.Monitor
for mosquito larvae during periods when water levels remain low, or when water
levels fluctuate frequently.

Areas designed to infiltrate, rather than hold, storm water
can also become potential mosquito breeding areas.If these infiltration areas remain wet for
periods longer than 72 hours, floodwater mosquitoes are often the first to
invade8.If poor management
has resulted in grass cuttings or polluted runoff accumulating in these wet
areas, vector mosquitoes can be found later in the summer season.Avoid placement of infiltration systems in
areas where they are likely to remain wet for longer than 72 hours (e.g. where
the water table is close to the surface).Storm water infiltration areas should be free of isolated depressions
that could allow water to accumulate for longer periods.Mowing near infiltration areas should be done
without producing ruts where water can collect, and grass clippings and debris
should be removed regularly.

Use of Chemical Products in Ponds to Control
Mosquitoes

Questions arise about the use of chemicals and other
products for mosquito control.Due to a
higher level of environmental and human health risk compared with natural
mosquito control methods, chemical controls should be seen as a last resort.Chemicals for mosquito control are best left
to certified pesticide applicators9.Before applying chemical controls, you should verify that the mosquito
population in question is at risk for transmitting disease.For more information see the Purdue Extension
publication E-52-W, Mosquito Control by
Trained Personnel, http://www.entm.purdue.edu/Entomology/ext/targets/e-series/EseriesPDF/E-52.pdf

Wetlands and mosquitoes:

Natural Wetlands

Management practices that ensure healthy, functioning
aquatic ecosystems are proven long-term and cost-effective strategies for
controlling mosquito populations.Contrary
to popular belief, natural wetlands can reduce the population of mosquitoes
compared with drained or degraded wetland areas.According to the Indiana Department of
Natural Resources-Division of Fish & Wildlife, wetland restoration
decreases mosquito populations in two ways: by providing healthy habitat for
the natural enemies of mosquitoes, and by preventing or reducing flooding in
non-wetland areas.The IDNR fact sheet, “Did
you know? Healthy wetlands devour mosquitoes”
(http://www.in.gov/dnr/fishwild/publications/inwetcon/hlywet.pdf), provides an
example of one mosquito control project that documented a reduction of 90
percent in the mosquito population after restoring a 1,500 acre wetland area10.

To be certain, all wetlands will have populations of
mosquitoes varying with the degree of wetness and air temperature.During drought periods when water in some
wetland areas may be reduced to small or shallow pools, mosquitoes can migrate
and congregate in these smaller areas of wetness, though populations of flood
water mosquitoes overall tend to decrease during drought periods 11, 12.However, in areas where wetlands have been
drained mosquito populations thrive when these former wetland areas become inundated
after rain storms10.Following
rain, intermittent moist muddy or shallow stagnant water combined with an
absence of predators of mosquitoes can allow the mosquito population to explode
10,11,12,13, including disease carrying mosquitoes that breed only in
stagnant water 11.This type
of flooding in non-wetland areas occurs more frequently afterwetlands are drained and this creates
the most serious nuisance mosquito problems in Indiana10.The Indiana Department of
Natural Resources recommends restoring these wetland ecosystems10.For additional information on wetlands see
the Purdue Extension publication Wetlands and Water Quality WQ-10 http://persephone.agcom.purdue.edu/AgCom/Pubs/WQ/WQ-10.html.

Long-term commitment to wetland restoration also saves tax
payers money on mosquito control.A
study of a 548 acre marsh in 1969 on the U.S.
east coast reported spending $16,000 to implement wetland restoration.Since that time the wetland has not needed
any maintenance, cleaning, pesticides, or other costs.It was estimated that in a 25 year period
since 1969 traditional insecticide methods would have cost $685,00010, 14, 15.

Constructed Wetlands:

“Artificial” wetlands are being constructed in Indiana
to control and treat storm water and wastewater.Whenever possible, constructed wetlands that
treat wastewater should be located away from residential areas and beyond the
flight range of local disease carrying mosquitoes.Locating constructed wetlands in open areas
where wind can produce waves in the wetland will disrupt mosquito development.

Pollutant traps and sedimentation zones within the wetland
should be managed to prevent blockages and pollutant buildup, as blockage can
promote stagnant water.Maintaining
water movement through the wetland is important for reducing mosquito
populations.Riffle zones provide
turbulence detrimental to mosquito larvae and also raise oxygen levels in the
water.

Water
reservoirs other than ponds and wetlands where mosquitoes may breed (Listed alphabetically)

Checkif present:

Date problem
remedied:

Basements with standing water

q

Birdbaths

q

Boats that have not been drained or covered

q

Cans, jars, other open containers

q

Clogged house roof gutters

q

Culverts with stagnant water

q

Ditches that hold stagnant water

q

Drain outlets from air-conditioners

q

Dripping outdoor faucets

q

Flower pots

q

Leaf-filled drains

q

Leaking pipe joints

q

Livestock water tanks

q

Manure treatment lagoons

q

Old cisterns

q

Ornamental ponds

q

Over-irrigated lawns and fields

q

Saucers under potted plants

q

Septic absorption fields (if soggy)

q

Sewage treatment ponds

q

Standing water in tire ruts and horse or livestock
lots

q

Storm water drain systems

q

Street gutters, catch basins at road corners

q

Stumps and tree holes

q

Swimming pool covers

q

Tires (abandoned)

q

Unsealed barrels

q

Wading pools or kiddie
pools

q

Water cans, buckets, troughs, pet bowls

q

Wheel barrows or tilt-up carts

q

Wells in old frost pits that flood

q

Aeration systems for large constructed wetlands reduce
mosquito larvae by disturbing the water surface, and sprinkler systems can inhibit
mosquito egg laying.If constructed wetlands become over-vegetated they provide ideal habitat
for mosquito larvae due to being protected from predators and from rainfall and
wave action.Maintenance of vegetation
by harvesting and culling of plants can provide for increased water movement
and predator access to mosquito larvae.

Managing water other than ponds and wetlands near the
home:

Mosquitoes that tend to lay their eggs in human-made
reservoirs near residential areas are the primary disease carrying species, and
are often referred to as vector mosquitoes 11, 16,17,
18, 19.More information on vector
mosquitoes can be read online at http://www.entm.purdue.edu/Entomology/ext/targets/e-series/EseriesPDF/E-204.pdf .If you have
a mosquito problem around your home, chances are good that they are breeding in
your yard.

The number one action that homeowners can take to reduce
vector mosquitoes near the home is to eliminate the reservoirs where these
mosquitoes often breed20.The
checklist on this page, “Water reservoirs
other than ponds and wetlands where mosquitoes may breed”, provides a
general list of these breeding areas.Consider
that just one inch of water in an ordinary coffee can may
result in as many as 1,000 mosquitoes every seven days.For a photographic chart of the life cycle of
a vector mosquito visit the Mosquito
Hygiene web site http://www.cfe.cornell.edu/erap/WNV/WNVEducDocs/MosqHygienePoster6-02.pdf

In many cases, simply altering the reservoir will prevent
mosquito breeding, for example turning a wheel barrow upside down to prevent
pooling of stagnant water.In other
instances, the reservoir should be eliminated, as in the case of abandoned
tires.Regular maintenance is required
for some reservoirs, such as keeping rain gutters cleaned of debris, and
changing water in bird baths and pet bowls once a week.There are additional problem areas that fall
into the jurisdiction of county and city officials, such as storm water drains
and ditches.Contact your local health
department for information and assistance.

For more information on mosquitoes and their control around
the home refer to Purdue Extension publication, E-26-W, Mosquitoes In and Around the Home,
http://www.entm.purdue.edu/Entomology/ext/targets/e-series/EseriesPDF/E-26.pdf.

An issue that deserves further inquiry

Ponds, wetlands, and residential environments in relation to
mosquitoes are complex issues.This
publication presents available information and strategies for pond, wetland,
and water reservoir management as a way of helping Indiana
residents to minimize mosquito problems.Further studies focused on the effects of protecting and encouraging
natural predators of mosquitoes through ecosystem restoration would shed light
on some of these complex issues.Currently,
only four percent of natural wetland areas in Indiana
remain.As wetland areas are restored
mosquito populations and predator: prey relationships can be monitored.This publication will be updated as knowledge
on this issue evolves.

Assistance with pond and wetland restoration and
management

Technical assistance is available from the agencies listed
below.Some cost-share funds, as well as
payment programs on agricultural lands, may be available for pond and wetland
restoration and protection.

6Offill, Y.A. and W.E. Walton. 1999. Comparative efficacy of the threespine
stickleback (Gasterosteusaculeatus)
and the mosquito fish (Gambusiaaffinis)
for mosquito control. Journal of the American Mosquito Control Association
15(3): 380-390.